The invention relates to an approach detection device having a sensor system for detecting the approach of a user. In particular the invention relates to approach detection devices having a capacitive approach sensor.
Capacitive sensors, or corresponding systems are known from the prior art, and can detect the approach of a user without physical contact. For this, the change in the capacity of an electrode assembly is measured, wherein the capacity is a function of the distance of a body part of the user to the electrode assembly. An electrode assembly of this type is described, for example, in DE 10 2005 061 755 A1.
Capacitive sensor systems are used in “Passive Entry” systems, among others, in which the user no longer needs to actively actuate a button on a remote control unit in order to open a vehicle. Instead, it is sufficient for the user to carry a remote control, also known as an ID provider (identification provider). As soon as a user approaches an approach detection device, this approach is detected by the capacitive approach sensor, upon which a control device disposed in the motor vehicle transmits a radio signal to the ID provider via a transmitting antenna, which awakens the ID provider from the so-called “sleep mode.” Reception of the wake-up signal initiates a radio signal dialog between the ID provider and the control device for the motor vehicle, with which the authorization, or non-authorization, respectively, from the ID provider is ascertained for opening the motor vehicle. Insofar as the authorization of the ID provider is ascertained in the course of the radio signal dialog, a lock in the motor vehicle, allocated to the sensor system, is unlocked, such that a lock (door lock, trunk, engine hood) can be opened by a subsequent actuation of a handle, or the execution of a specific gesture.
The typically used capacitive approach sensors are strongly dependent on environmental conditions; humidity, condensation and other influences can impact the capacity of the sensor system, such that the detection of the approach of a body part of the user is impeded due to the disturbances.
By way of example, door handle systems in which capacitive approach sensors are used, which are protected against environmental influences, are described in the prior art. By way of example, EP 03 100 728.9 discloses a system in which the capacitive sensor assembly is disposed behind a housing wall. The space between the sensor assembly and the housing wall is filled with an electrically insulating material, in order to prevent the entry of moisture or other contaminants that could affect the capacity of the sensor system.
In particular in the proximity of the electrodes in the capacitive sensor, the impact of disturbing effects is to be prevented as much as possible. For this, it has been suggested in the prior art to embed capacitive sensors in a casting compound, in order to thus prevent a direct influence on the sensor surfaces. According to this prior art, the entire space between a cast electrode assembly of this type and a wall of a door handle is filled with insulating material.
The disadvantage with this system, however, is that the impact of the material, even if it keeps damaging effects away from the detection region of the capacitive sensor, is detrimental to the detection sensitivity of the capacitive sensor. Although the material is electrically insulating, the capacity is nevertheless affected by this dielectric medium.
The disadvantage with the solutions according to the prior art is, furthermore, that the components used therein must be manufactured specifically for one sensor device, meaning that they cannot be used in similar systems. Accordingly, specialized components must be produced for each application, which increases the costs for the known devices.
The objective of the invention is to create a universally applicable approach detection device that is protected against environmental influences.